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The impact of decreasing plant diversity on terrestrial ecosystem productivity remains controversial. Recent studies generally suggest that diverse plant communities are more productive than depauperate versions. However, there is less agreement as to whether this is caused by the number of species present, the identities of the species present, the number of functional groups that these species make up, or by which functional groups are represented. This study evaluates whether relationships between plant diversity and productivity in northern mixed grass prairie are dependent on (a) the diversity measure used (species richness vs. functional richness), (b) the productivity measure utilized, or (c) the scale of observation. We collected plant diversity and productivity information over circular plots of 0.5 m diameter during the summer of 1998, then used a spatially nested sampling design to scale each property and their relationships to 2.5 m, 10 m and 50 m sampling resolutions. Observed diversity-productivity relationships were dependent on all of the above factors. Richness-productivity relationships were found to be mostly asymptotic at all observational scales. The presence of particular species, and functional groups, alone or in combination all had significant effects on productivity at the plot (0.5m) level, but not at coarser resolutions. These results were consistent with those of other studies, and suggest that the higher productivities of diverse grassland plots in our grassland site might result from the effects of diversity and the presence of productive species. The lack of species effects at coarser resolutions suggest other mechanisms are responsible for such relationships at these scales.

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Agrokémia és Talajtan
Authors:
Krisztina Végh
,
J. Csillag
,
A. Lukács
,
B Panwar
, and
Gy. Füleky

Potassium uptake is the result of numerous simultaneous processes influencing the potassium dynamics in the rhizosphere.The presented research has focused on plant-soil interactions in the potassium supply of soil in the root environment of maize. It was assumed that: 1. roots promote the mobilization of K by the acidification of the rhizosphere soil, 2. roots increase wetting-drying cycles in their environment, and 3. soil total K content affects K release and fixation in the bulk of soil and the root environment.The promoting effect of root activity was detected on K release from soil when feldspar was added as K source to the root environment. A 2-unit reduction of soil pH multiplied K concentration in the soil solution, depending on the feldspar rate. Feldspar application significantly increased the solubility and release of potassium into the soil solution.The effect of pH reduction on the K concentration of soil solution was several magnitudes higher than that of the wetting-drying cycles both in the untreated and feldspar treated soils.Potassium uptake by maize over two generations greatly exceeded the exchangeable pool in the growing media. As a consequence of the exhaustive K uptake K release slowed down to the soil solution, as reflected in the H2O extractable K and ExK contents.Significant K fixation was detected after the K removal of maize in feldspar treated soils. On the contrary, in the treatments without plants increasing feldspar rates increased both H2O extractable K and ExK contents.One-term Langmuir equation, corrected with the originally sorbed amount of K, was fitted to measured data. The maximum amount of potassium adsorption (Kmax, mg∙kg−1) and the equilibrium constant (k) were calculated. The potassium buffering capacity was estimated at zero equilibrium concentration. Both K buffering capacity and the energy of K fixation were high for the rhizosphere soil. In rhizosphere soil samples the energy of K fixation was one magnitude higher as compared to the bulk soil and decreased substantially with feldspar addition. In soils without plants the k equilibrium constant did not change as the result of drying-wetting process only in the case of the 50% soil/feldspar mixture.In the liquid phase of the soil without feldspar application potassium concentration decreased in the one-year drying-wetting cycle, presumably it got into more strongly bounded forms in the low K status soil. In 50% feldspar enriched soil samples potassium concentration in the soil solution increased, likely as a consequence of a slow dissolution of the K content of feldspar.

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Cereal Research Communications
Authors:
K. Végh
,
E. Osztoics
,
P. Csathó
,
J. Csillag
,
L. Radimszky
,
G. Baczó
,
M. Magyar
,
T. Takács
,
A. Lukács
, and
M. Karátsonyi
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Agrokémia és Talajtan
Authors:
Péter Csathó
,
E. Osztoics
,
J. Csillag
,
T. Lengyel
,
L. Gonda
,
L. Radimszky
,
G. Baczó
,
M. Magyar
,
K. R. Végh
,
M. Karátsonyi
,
T. Takács
,
A. Lukács
, and
T. Németh

Depending on their origin, sedimentary phosphate rocks (PRs) may differ in their P solubility, and, as a consequence, in their agronomic effectiveness. The effect of six phosphate rocks (PR) - originating from Algeria (ALG), North Florida (FLO), North Carolina (NCA), Senegal (SEN) Morocco (MOR) and Hyperphosphate (HYP) with various P solubility (evaluated by 2% formic acid, 2% citric acid, and neutral ammonium citrate) - as well as single superphosphate (SSP) and superphosphate + lime (SSP + Ca) (each P source on 4 P levels, with doses of 0, 100, 400 and 1600 mg P 2 O 5 ·kg -1 soil) on the shoot yield of tillering stage spring barley, soil available P (i.e. H 2 O, Olsen, Bray1, Lakanen-Erviö (LE) and ammonium lactate (AL) extractable P contents) were studied in pot experiments set up with acidic sandy soil (Nyírlugos, Hungary) and acidic clay loam soil (Ragály, Hungary), both with low P supplies.  The average spring barley shoot yield at the beginning of shooting was 95% higher on the colloid-rich acidic (pH KCl : 4.5) clay loam soil than on the colloid-poor acidic (pH KCl : 3.8) sandy soil. The differences in the solubility of phosphate rocks showed close correlation to the differences in P responses. On both soils, the correlation between total PR-P added and P responses in spring barley shoot yield was much weaker than that between neutral ammonium citrate soluble PR-P added and P responses in spring barley shoot yield. When phosphate rocks were applied as P sources, the comparison of soil test P methods showed a different picture on the two soils. In the case of the acidic sandy soil (Nyírlugos), the strongly acid LE-P (r² = 0.83) and AL-P (r² =0.74) tests gave the highest correlation coefficients with spring barley responses to P, while on the acidic clay loam soil (Ragály) these were achieved by the Olsen-P (r² = 0.88) and Bray1-P (r² =0.88) methods. 

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